The present invention relates to propylene polymers, optionally containing up to 5 mol % of ethylene, having a number of internal vinylidene unsaturations per polymer chain greater than or equal to 2; these polymers are obtained by removing at least a part of hydrogen present in the polymerization apparatus during the process.
It is known that polypropylene, although possessing good physicomechanical properties and excellent chemical resistance, lack highly desirable properties, such as varnishability, dyeing adhesion and compatibility with other polymers or inorganic substrates because of the apolar and saturated nature. Introducing a high number of unsaturations in the polymer chain therefore could be a way for obtaining a functionalizable polymer and for eliminating these disadvantages. It is known that the polymerization of olefins carried out with metallocene complexes gives rise to evolution of molecular hydrogen. For instance J. Am. Chem. Soc. 1998, 120, 2174-2175 shows that gas-phase reactions between ethylene or an alpha-olefin and Cp2ZrCH3+ during mass spectroscopic studies result in elimination of molecular hydrogen with concomitant formation of an eta-3-allyl complex. This evolution has been associated with the formation of unsaturations in the polymer chain. Formation of internal unsaturations in the polymer chain in ethylene/alpha-olefin copolymers produced with metallocenes is reported in Polymers Preprints 1998, 39(2), 425. However these documents do not relate to propylene polymerization and moreover, in these documents, there is no indication that the nature and the number of internal unsaturation in a propylene polymer may be controlled. Chain transfer reactions in polypropylene polymerization have been investigated by Resconi at al. in Topics in Catalyst 1999, 7, 145-163, but he does not relate to hydrogen produced during the polymerization reactions.
EP 778293 relates to a process for producing an olefin polymer where an olefin is polymerized in the presence of a metallocene complex; by forced removing hydrogen during the polymerization process, it is possible to obtain an olefin polymer having a desired melt index. In this document the presence of hydrogen in the process is explained by the formation of unsaturated bonds at the terminal end of olefin polymer, no reference being made to internal unsaturations; moreover only ethylene/1-hexene is polymerized in the examples. The Applicant has now unexpectedly found a new propylene polymer, optionally containing up to 5 mol % of ethylene, having the following characteristics:
i) molecular weight distribution (MW/Mn)xe2x89xa64;
ii) number of internal vinylidene per polymer chain xe2x89xa72.
The propylene polymer object of the present invention is obtainable with a polymerization process carried out in the presence of a metallocene-based catalyst system, by selectively removing at least part of hydrogen present in the polymerization apparatus during the polymerization process. More specifically, it is another object of the present invention a process for preparing the above described propylene polymers comprising contacting, under polymerization conditions, propylene and optionally ethylene, with a catalyst system comprising:
a) a metallocene complex of formula (I) 
xe2x80x83wherein:
M is titanium zirconium or hafnium; preferably M is zirconium;
the groups X equal to or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, xe2x80x94R, xe2x80x94OR, xe2x80x94OCOR, xe2x80x94OSO2CF3, xe2x80x94SR, xe2x80x94NR2 and xe2x80x94PR2, wherein R is a linear or branched C1-C20 alkyl, C2-C20 alkenyl C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radical; preferably R is methyl, ethyl, propyl, butyl or phenyl; preferably X is halogen or C1-C20 alkyl;
the groups R1, R2, R3 and R4, equal to or different from each other, are selected from the group consisting of hydrogen, linear or branched C1-C20 alkyl, C2-C20 alkenyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radicals, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table; two or four adjacent groups R1, R2, R3 and R4 may form together one or more 3-6 membered aromatic or aliphatic rings, optionally substituted with hydrocarbyl radicals optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table; preferably R1, R2, R3 and R4 are hydrogen or C1-C20 alkyl; optionally containing nitrogen, phosphorus or sulfur, or R1 and R2 form a six-membered aromatic or aliphatic ring;
with the proviso that either R1 is different from R4 or R2 is different from R3;
Z is a carbon or silicon atom; preferably Z is a carbon atom;
the groups R1 and R6, equal to or different from each other, are selected from the group consisting of hydrogen, linear or branched C1-C20 alkyl, C2-C20 alkenyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radical optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table; R5 and R6 optionally form together a 3 to 6-membered ring; preferably R5 and R6 are selected from the group consisting of hydrogen, methyl, ethyl, propyl and phenyl; and
b) a suitable activating cocatalyst;
said process being characterized by reducing the concentration of hydrogen formed during the polymerization reaction
The number of internal vinylidenes per polymer chain is defined as the number of internal vinylidene bonds over the total number of unsaturated end groups. More precisely, the number of internal vinylidenes per polymer chain is the ratio between the number of bonds in a polymer chain having the following structure: 
over the total number of unsaturated end groups in a polymer chain, having the following structures: 
Using N.M.R. techniques, the skilled man in the art can carry out the analysis of the polymer in order to determine the content of internal vinylidene per polymer chain. Examples of N.M.R. assignments can be found in Topics in Catalysis 1999, 7, 145 and Journal of Molecular Catalysis 1999, 146, 167.
The propylene polymer, optionally containing up to 5 mol % of ethylene, object of the present invention has the following characteristics:
(i) molecular weight distribution (MW/Mn) xe2x89xa64, preferably xe2x89xa63,
xe2x80x83more preferably xe2x89xa62.5;
(ii) number of internal vinylidene per polymer chain xe2x89xa72, preferably xe2x89xa72.5, more preferably xe2x89xa73.
Moreover, according to a preferred embodiment, the propylene polymers of the invention have the following characteristic:
iii) the isotactic pentads (mmmm), as determined by 13C-NMR analyses, are xe2x89xa780%.
According to another preferred embodiment, the propylene polymer of the invention, have the following characteristic:
iv) less than 0.5% of the CH2 groups in the polymeric chain are in sequences (CH2)n wherein n is an even number. The structure of the propylene polymer according to the invention appears to be highly regioregular. In fact, from the 13C-N.M.R. analysis (125.7 MHz) no signals are revealed as deriving from the (CH2)n sequence where n is an even number.
Preferably the propylene polymers, object of the present invention, are obtainable by a process comprising contacting, under polymerization conditions, propylene and optionally ethylene with a catalyst system comprising:
a) a metallocene complex of formula (II) 
xe2x80x83wherein
M, X, R3, R4, R5 and R6 have the meaning reported above and the groups R7, R8, R9 and R10, equal to or different from each other, are selected from the group consisting of hydrogen, linear or branched C1-C20 alkyl, C2-C20 alkenyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing heteroatoms belonging to groups 13-17 of the Periodic Table; preferably R7, R8, R9 and R10 are hydrogen, C1-C20 alkyl or C6-C20 aryl;
preferably R3 is a group SiR3 or CR3, wherein R has the meaning reported above, R4 is hydrogen; more preferably R3 is Si(CH3)3 or C(CH3)3; and
b) a suitable activating cocatalyst;
said process being, characterized in that the concentration of the hydrogen formed during the polymerization reaction is reduced.
Metallocene complexes can be obtained with various processes known in the art such as, for example, as described in WO 96/22995 and WO 98/43989.
In the process of the invention, hydrogen can be suitably removed during the polymerization reaction by means of methods known in the art, such as:
1) by using a hydrogenation catalyst in the gas phase, able to catalytically hydrogenate olefins;
2) by using a hydrogenation catalyst in the liquid phase, able to catalytically hydrogenate olefins;
3) by physically removing hydrogen from the gas phase.
According to methods 1) and 2), hydrogen present in the polymerization reactor reacts with propylene monomer to produce propane. As a result, the concentration of hydrogen gas in the reaction system is decreased. At this time, the amount of the propane produced is small and it has substantially no adverse effect on the polymerization of propylene.
Examples of hydrogenation catalysts fit for method 1) are platinum- or palladium-based compositions, particularly preferred is platinum or palladium on alumina.
Preferably these catalysts are installed in the gas cap of the reactor.
Examples of hydrogenation catalysts fit for method 2) are cobalt- or nickel-based catalysts activated by trialkylaluminiums, such as cobalt(acetylacetonate) or nickel(octanoate); rhodium catalysts such as Wilkinson""s catalyst (Rh(PPh3)3Cl); ruthenium catalysts, such as Ru(H)Cl(PPh3)3. Alternatively heterogeneous platinum, platinum oxide or palladium catalysts may be used as a suspension in the reaction medium.
Hydrogenation catalysts which can be used for methods 1) and 2) are described in xe2x80x9cCatalytic Hydrogenationxe2x80x9d (R. L. Augustine, publisher Dekker, New York, 1965) and in xe2x80x9cAdvanced Organic Chemistryxe2x80x9d, 4th Edition, p. 771-780 (J. March, publisher Wiley, New York, 1992). Once selected the hydrogenation catalyst, those skilled in the art can select the necessary amount of it depending on the catalyst activity, according to common procedures.
According to method 3), hydrogen can be physically removed from the reactor by using, for example, a solid or a liquid adsorbent which can selectively adsorb hydrogen or a hydrogen separating membrane that allows hydrogen to permeate; alternatively the gas cap of the reactor can be vented. The hydrogen concentration during the polymerization reaction, is reduced to less than 50%, preferably to less than 30% and more preferably to less than 20% of the hydrogen concentration in absence of means to reduce it (hydrogenation catalysts or physical means).
In other words, the hydrogen concentration in the reactor in the presence of hydrogenation means has to be less than 50% preferably less than 30% more preferably less than 20% of the hydrogen concentration that would be in the reactor under about the same reaction conditions but in absence of means for removing hydrogen. When the polymerization reaction is carried out in liquid phase, hydrogen concentration in the gas phase of the reactor (i.e. in the gas cap) can vary from 0 to 0.020% mol. more preferably from 0 to 0.015% mol.
Suitable activating cocatalysts according to the process of the invention are alumoxanes or compounds capable of forming an alkyl metallocene cation.
Alumoxane useful as cocatalyst (b) may be linear alumoxanes of the formula (III): 
wherein R11 is selected from the group consisting of halogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals and y ranges from 0 to 40;
or cyclic alumoxanes of the formula (V): 
wherein R11 has the meaning herein described and y is an integer ranging from 2 to 40.
The above alumoxanes may be obtained according to procedures known in the state of the art, by reacting water with an organo-aluminum compound of formula AlR113 or Al2R116, with the condition that at least one R11 is not halogen. In this case, the molar ratios of Al/water in the reaction is comprised between 1:1 and 100:1. Particularly suitable are the organometallic aluminum compounds described in formula (II) of EP 0 575 875 and those described in formula (II) of WO 96102580. Moreover, suitable cocatalysts are those described in WO 99/21899 and in the European app. no. 99203110.4.
The molar ratio between aluminum and the metal of the metallocene complex is comprised between about 10:1 and about 20000:1, preferably between about 100:1 and about 10000:1, more preferably between 100:1 and about 5000:1.
Examples of alumoxanes suitable as activating cocatalysts in the process of the invention are methylalumoxane (MAO), tetra-isobutyl-alumoxane (TIBAO), tetra-2,4,4-trimethylpentyl-alumoxane (TIOAO) and tetra-2-methyl-pentylalumoxane. Mixtures of different alumoxanes can also be used. Not limiting examples of aluminum compounds of formula AlR113 or Al2R116 are:
tris(methyl)aluminum, tris(isobutyl)aluminum, tris(isooctyl)aluminum, methyl-bis(isobutyl)aluminum, dimethyl(isobutyl)aluminum, tris(isohexyl)aluminum, tris(benzyl)aluminum, tris(tolyl)aluminum, tris(2,4,4-trimethylpentyl)aluminum, bis(2,4,4-trimethylpentyl)aluminum hydride, isobutyl-bis(2-phenyl-propyl)aluminum, diisobutyl-(2-phenyl-propyl)aluminum, isobutyl-bis(2,4,4-trimethyl-pentyl)aluminum, diisobutyl-(2,4,4-trimethyl-pentyl)aluminum, tris(2,3-dimethyl-hexyl)aluminum, tris(2,3,3-trimethyl-butyl)aluminum, tris(2,3-dimethyl-butyl)aluminum, tris(2,3-dimethyl-pentyl)aluminum, tris(2-methyl-3-ethyl-pentyl)aluminum, tris(2-ethyl-3-methyl-butyl)aluminum, tris(2-ethyl-3-methyl-pentyl)aluminum, tris(2-isopropyl-3-methyl-butyl)aluminum, tris(2,4-dimethyl-heptyl)aluminum, tris(2-phenyl-propyl)aluminum tris(2-(4-fluoro-phenyl)-propyl)aluminum and tris(2-(4-chloro-phenyl)-propyl)aluminum
as well as the corresponding compounds where one or more of the hydrocarbyl groups is replaced by a hydrogen atom.
Particularly preferred aluminum compounds are trimethylaluminum (TMA), tris(2,4,4-trimethylpentyl) aluminum (TIOA), triisobutylaluminum (TIBA), tris(2,3,3-trimethyl-butyl)aluminum, tris(2,3-dimethyl-butyl)aluminum, tris(2-phenyl-propyl) aluminum, tris[2-(4-fluoro-phenyl)-propyl]aluminum and tris[2-(4-chloro-phenyl)-propyl]aluminum. Mixtures of different organometallic aluminum compounds and/or alumoxanes can also be used. In the catalyst system used in the process of the invention, both said metallocene complex and said alumoxane can be pre-reacted with an organometallic aluminum compound of formula AlR113 or Al2R116, wherein R11 has the meaning reported above.
Further suitable cocatalysts are those compounds capable of forming an alkylmetallocene cation; preferably, said compounds have formula Y+Dxe2x88x92, wherein Y+ is a Brxc3x8nsted acid capable of donating a proton and of reacting irreversibly with a substituent X of the compound of formula (I) or (II), and Dxe2x88x92 is a compatible non-coordinating anion, capable of stabilizing the active catalytic species which result from the reaction of the two compounds, and which is sufficiently labile to be displaceable by an olefinic substrate. Preferably, the Dxe2x88x92 anion comprises one or more boron atoms. More preferably, the anion Dxe2x88x92 is an anion of formula BAr4(xe2x88x92), wherein the Ar substituents, the same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl-borate is particularly preferred. Moreover, compounds of formula BAr3 can be conveniently used. The process for obtaining the propylene polymer of the present invention can also be carried out by depositing the metallocene complex of formula (I) or (II) or the reaction product of the the metallocene complex of formula (I) or (II) with a suitable cocatalyst, or the suitable cocatalyst and successively the metallocene complex of formula (I) or (II), on the inert support, such as silica, alumina, magnesium halides, olefin polymers or prepolymers (i.e. polyethylenes, polypropylenes or styrene-divinylbenzene copolymers). The thus obtained supported catalyst system, optionally in the presence of alkylaluminum compounds, either untreated or pre-reacted with water, can be usefully employed in gas-phase polymerization processes. The solid compound so obtained, in combination with further addition of the alkyl aluminum compound as such or prereacted with water, is usefully employed in gas phase polymerization. The polymerization process according to the present invention can be carried out in gaseous phase or in liquid phase, optionally in the presence of an inert hydrocarbon solvent either aromatic (such as toluene), or aliphatic (such as propane, hexane, heptane, isobutane and cyclohexane).
The polymerization temperature ranges from about 0xc2x0 C. to about 250xc2x0 C., preferably from 20xc2x0 C. to 150xc2x0 C., and more preferably from 40xc2x0 C. to 90xc2x0 C.
The molecular weight distribution can be varied by using mixtures of different metallocenes or by carrying out the polymerization in various steps differing in the polymerization temperature and/or in the concentration of the polymerization monomers.
Metallocene complex of formula (I) or (II) and the suitable cocatalyst may be contacted among them before the polymerization. The contact time may be comprised between 1 and 60 minutes, preferably between 5 and 20 minutes. The pre-contact concentrations for metallocene complex of formula (I) or (II) are comprised between 10xe2x88x922 and 10xe2x88x928 moll, whereas for the suitable cocatalyst they are comprised between 10 and 10xe2x88x923 mol/l. The precontact is generally carried out in the presence of a hydrocarbon solvent and, optionally, of small amounts of monomer. The propylene polymers of the present invention can be crosslinked either by electron beam irradiation or with chemical reagents. The propylene polymers of the present invention are suitable for various kinds of applications, such as insulated wire and other electric parts, printed circuit boards, heat insulating materials, packaging materials and roofing materials, by introduction of functional groups by chemical means into the hydrocarbon structure for further advanced applications. A further advantage of the propylene polymers of the present invention is that the internal vinylidene unsaturations are not subjected to thermal degradation or oxidative degradation if compared with polyolefins having unsaturations on the backbone. The following examples are given for illustrative purposes and are not intended to limit the scope and spirit of the invention.